Asphalt is one of the world's oldest engineering materials, having been used since the beginning of civilization. Asphalt is a strong, versatile and chemical-resistant binding material that adapts itself to a variety of uses. For example, asphalt is used to bind crushed stone and gravel into firm tough surfaces for roads, streets, and airport runways. Asphalt, also known as pitch, can be obtained from either natural deposits, or as a by-product of the petroleum industry. Natural asphalts were extensively used until the early 1900s. The discovery of refining asphalt from crude petroleum and the increasing popularity of the automobile served to greatly expand the asphalt industry. Modern petroleum asphalt has the same durable qualities as naturally occurring asphalt, with the added advantage of being refined to a uniform condition substantially free of organic and mineral impurities.
The raw material used in modern asphalt manufacturing is petroleum, which is naturally occurring liquid bitumen. Asphalt is a natural constituent of petroleum, and there are crude oils that are almost entirely asphalt. The crude petroleum is separated into its various fractions through a distillation process. After separation, these fractions are further refined into other products such as asphalt, paraffin, gasoline, naphtha, lubricating oil, kerosene and diesel oil. Since asphalt is the base or heavy constituent of crude petroleum, it does not evaporate or boil off during the distillation process. Asphalt is essentially the heavy residue of the oil refining process.
Because asphalt is a residue from an oil refining process, if a blend of oils from more than one crude source is used as an input, the resulting asphalt residue will also represent a combination of the oils. Due to lower reliability of resulting asphalt quality prediction, proportions of individual crudes in the slate cannot be economized and a quality buffer is typically required. In the other words, a blend of feeds is selected that is conservative on quality, such as by using a higher percentage of heavy asphaltic feeds than is strictly needed, in order to increase the likelihood of meeting the asphalts specifications after manufacturing is done. However, having to select a heavier blend of feeds to form a desired asphalt can cause difficulties in other parts of a refinery, as using the heavier crudes that typically produce higher quality asphalt can limit the distillation throughput for the refinery.
Although individual asphalts can be characterized relative to a cut point temperature for separating heavy oil from the asphalt residue, conventional methods of characterizing blends of asphalts have been only partially successful. As a result, when a blend of oils is used to form an asphalt, the asphalt is usually characterized experimentally to determine all or nearly all specifications that determine the suitability of an asphalt for various potential uses. During this characterization time, storage tanks or another means for holding the asphalt prior to sale are required. If sufficient storage is not available, it may result in the slowing or even stopping of one or more additional refinery processes until the asphalt can be characterized and assigned a grade for sale.